1. Field of the Invention
The present invention relates to a process for producing a polymer/filler composite material, and more specifically it relates to a process for production of a polymer/filler composite material containing a flake-like filler (plate-like filler) which can give film materials and foam bodies with excellent properties such as flexural modulus, strength and impact resistance.
2. Related Background Art
It has been attempted in the past to improve the physical properties and moldability of polymer materials by adding fillers to the polymer materials. In recent years, flake-like fillers derived from layered clay minerals (multi-layered clay minerals) and the like have been the subject of focus as fillers for addition to polymer materials, and for example, U.S. Pat. No. 5,717,000 discloses a polymer foam body obtained by adding an organophilic layered clay mineral with a polyolefin or the like and then foaming it with a foaming agent.
However, polymer/filler composite materials produced by the process disclosed in the aforementioned publication and other publicly known art publications have not always exhibited adequate properties such as flexural modulus, strength and impact energy. The present inventors attribute the problems of the art to the fact that the dispersed state of the filler in the polymer material is not sufficiently controlled, and no method has been known in the art for dispersion of flake-like fillers such as layered clay minerals in polymer materials in a uniformly regular manner.
The present invention was accomplished in light of these circumstances, and its object is to provide a polymer/filler composite material wherein the dispersed state of the flake-like filler in the polymer material can be controlled, thus allowing production of a polymer/filler composite material with excellent properties such as flexural modulus, strength and impact resistance.
As a result of much diligent research directed toward achieving the object stated above, the present inventors have completed the present invention upon finding that by deforming at a specific strain rate a polymer material having a flake-like filler of a specific size dispersed therein at a specific concentration, it is possible to obtain a polymer/filler composite material with excellent properties such as flexural modulus, strength and impact resistance.
Specifically, the process for producing a polymer/filler composite material according to the invention is characterized by comprising:
forming a mixture of a flake-like filler and a polymer material, wherein the mean area (L2), mean thickness (d) and volume fraction (c) of the flake-like filler in the mixture satisfy the following equations (1), (2) and (3):
500 nm2xe2x89xa6L2xe2x89xa6100 xcexcm2xe2x80x83xe2x80x83(1)
dxe2x89xa6L/20xe2x80x83xe2x80x83(2)
0.2d/Lxe2x89xa6cxe2x89xa64d/Lxe2x80x83xe2x80x83(3),
and applying deformation to the mixture at a strain rate of no greater than 10 sxe2x88x921.
According to the production process of the invention, since a flake-like filler of a size satisfying the conditions of the above equations (1) and (2) is dispersed in a polymer material at a concentration satisfying the above equation (3), the mixture is able to exhibit rheopexy and strain hardening. Also, since the strain rate of the mixture is limited to no greater than 10 sxe2x88x921, the flake-like filler in the polymer material forms three-dimensional clusters. Here, three-dimensional clusters of the flake-like filler refers to formation of xe2x80x9chouse of card structuresxe2x80x9d by the flake-like filler in the polymer material, a model structure of which is shown in FIG. 1. According to the invention, formation of a house of card structure by the flake-like filler in the polymer material is believed to be responsible for the improvement in the properties of the polymer/filler composite material, such as flexural modulus, strength and impact resistance.
The house of card structure is a structure with the flake-like filler situated ideally with the normals to the flake-like filler sides oriented in the direction of the mutually intersecting x-axis, y-axis and z-axis (that is, the normals of the flake-like filler are mutually intersecting); however house of card structures also include cases where only two axial directions of the x-axis, y-axis and z-axis are in the relationship described above, as shown in FIG. 1. The concentration (number) of the flake-like filler may differ for each of the x-axis, y-axis and z-axis directions. Also, as shown in FIG. 2, it is sufficient if the flake-like filler normals are generally perpendicular, without all of them being perpendicular. That is, while it is ideal for the normals to the flake-like filler surfaces to be parallel to the x-axis, y-axis and z-axis, respectively, the normals and axes may deviate slightly from a parallel relationship, and a house of card structure according to the invention will be considered formed so long as the normals and axes form angles with an average of less than 45xc2x0 (preferably less than 30xc2x0 and more preferably less than 15xc2x0).
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.